1. Field of the Invention
The present invention relates to a high-frequency electronic device such as a television tuner.
2. Description of the Prior Art
A conventional high-frequency electronic device will now be described with reference to FIGS. 4 and 5. FIG. 4 is a perspective view of a conventional high-frequency electronic device and FIG. 5 is an explanatory diagram showing a circuit configuration of the conventional high-frequency electronic device.
In the conventional high-frequency electronic device, as shown in FIG. 4, a coaxial connector 22 is attached to one side face 21a of a shielding case 21 which houses high-frequency circuits therein, with a signal being inputted to the connector 22 from a coaxial cable (not shown). Within the shielding case 21, as shown in FIG. 5, there are provided high-frequency circuits such as a band pass filter 23 consisting of a high-pass filter and a low-pass filter, a first mixer 24, a second mixer 25, a first local oscillator 26 and a second local oscillator 27. Frequency conversion is performed twice by means of the first and second mixers 24, 25 and an intermediate frequency signal is outputted from the second mixer 25.
The high-frequency circuits provided within the shielding case 21 are each designed to be impedance-matched usually at 75 .OMEGA. (ohms) or 50 .OMEGA.. Therefore, the connector 22 is also designed to be 75 .OMEGA. or 50 .OMEGA. in characteristic impedance. A central conductor 22a of the connector 22 and the band pass filter are directly connected with each other, the connector and the band pass filter are impedance-matched, and a signal inputted to the connector 22 is applied to the band pass filter.
The coaxial cable connected to the connector 22 is designed to have a predetermined diameter (thickness) because it is necessary to diminish the transmission loss. Therefore, as the connector there is used one whose diameter corresponds to the diameter of the coaxial cable.
In the conventional high-frequency electronic device described above, the height of the side face 21a of the shielding case 21 with the connector 22 attached thereto cannot be made lower than the diameter of the connector 22. For this reason, it has so far been impossible to thin high-frequency electronic devices such as a television tuner to be mounted in a personal computer.
The purpose of thinning the devices can be achieved by using a coaxial connector of a small diameter. However, the use of a (thin) coaxial cable of a small diameter results in an increase in transmission loss of a received signal. On the other hand, using a coaxial cable of a large diameter requires the use of another connector for the connection of the connector 22 with the coaxial cable, thus leading to an increase in price of the high-frequency electronic device concerned.
In view of the above-mentioned problems it is an object of the present invention to provide a high-frequency electronic device capable of being reduced in thickness without deterioration of performance and increase of product cost.